This invention relates generally to vehicle occupant restraint systems in which an air bag is inflated to prevent the occupant from being thrown forwardly upon the occurance of sudden stoppage of the vehicle and more particularly to an improved aspirating inflator for such restraint systems.
Protective air bags that inflate to cushion the occupant for a vehicle from impact with the steering wheel, dashboard or other structural elements of a vehicle are well known. Deployment of the air bag is generally initiated by a sensor that is responsive to excessive deceleration of the vehicle. The air bag is generally inflated by igniting a combustible material or by releasing a gas and thereafter directing the combustion product or gas directly into the bag.
Automotive passenger restraint systems have evolved using two alternative inflation systems. One system comprises direct inflation wherein all of the gas used to inflate the bag originates in the gas source. The gas source may be pressurized gas, for example, air or nitrogen or a solid propellant.
Alternatively, the gas source may be combined with an aspirator. Current aspirated designs favor the use of a solid propellant, for example, a mixture of sodium azide and one of several oxidizers, in combination with an aspirator. In such aspirated designs, the inflating gas is augmented by air aspirated from the ambient air. Aspirator augmentation is advantageous in that a smaller gas source can be used, the final gas temperature is lower, and inflation is "softer" giving rise to lower impact forces on the vehicle occupant.
Conventional aspirator inflators typically use a solid propellant gas source that is contained within an aspirator housing. Flw of the propellant gas induces ambient air flow through orifices in a rear wall of the aspirator housing. Bulk pumping ratios, namely, the ratio of the weight of secondary gas (air) pumped to the weight of primary gas originating in the gas source, in the final bag gas composition are typically in the range of 0.1 to 0.5 for this type of inflator.
The foregoing construction is taught in U.S. Pat. No. 3,910,595 to Katter et al., which describes an aspirating airbag inflator that utilizes a plurality of gas generating cartridges. The gas generators are mounted on vertical struts in an aspirator duct. Air inlets and check valves are arranged in the rear wall of the duct in several different manners. Other prior art patents that teach the use of aspirating devices to inflate various devices are Freygang, U.S. Pat. No. 2,399,670; Allen, U.S. Pat. No. 2,595,218; Bowman et al., U.S. Pat. No. 2,866,593; Kane, U.S. Pat. No. 2,975,958; Wilmar, U.S. Pat. No. 3,040,970; Fraibel, U.S. Pat. No. 3,042,290; Marsh et al., U.S. Pat. No. 3,056,540 Galiger et al., U.S. Pat. No. 3,086,848; Young et al., U.S. Pat. No. 3,158,314; Hadler, U.S. Pat. No. 3,204,862; and Day, U.S. Pat. No. 3,370,784.
However, a problem still exists in maximizing the efficiency of an aspiration system designed for vehicle occupant protection.